Method of bonding using heat sealing protein adhesives



Patented June 17, 1952 METHOD OF BONDING USING HEAT SEALING PROTEINADHESIVES Arthur C. Beckel and John C. Cowan, Peoria, and Paul A.Belter, Pekin, Ill., assignors to the United States of America asrepresented by the Secretary of Agriculture No Drawing. ApplicationApril 5,1949, Serial No. 85,712

(Granted under the act of March 3, 1883, as

- amended April 30, 1928; 370 0. G. 757) 5 Claims.

This application is made under the act of March 3, 1883,, as amended bythe act of April 30, 1928, and the invention herein described, itpatented in any country, may be manufactured and used by or for theGovernment of the United States of America for governmental purposesthroughout the world without the payment to us of any royalty thereon.

This invention relates to protein adhesives, and in particular toadhesives comprising the waterextractable substances from soybeanmaterial tree from alcohol solubles. The invention has among its objectsto provide an adhesive coating comprising this water-extractablesubstance and various materials bonded therewith by heat energizing thedried coatings.

Still another object of this invention is the preparation of.proteinaceous adhesive coatings upon articles such as paper, wood,fabrics, metals, metal foil, regenerated cellulose sheeting and.

the like.

In application Serial No. 68,442, .filed Dec. 31, 1948, Arthur C. Beckeland Paul A. Belter disclose a soybean protein adhesive coating, usefulas a moisture-sensitive adhesive and which is also heat energi-zablewhile moist.

'We have now discovered that this material has a further unique propertywhich renders it particularly useful as a dry heat sealing adhesive.

In application Serial .No. 732,941, ."liled October 29,, 1947, nowPatent No. 2,495,706, Letta 1. De Voss, Arthur C. Beckel, and Paul A.Belter disclose a vegetable .gel manufactured by heating an aqueoussuspension of the water-extractable substance obtained from alcoholsolubles free soybean material.

According to that application, the spray dried solids from the waterextract may be dispersed in water and heated to temperatures of 150 F.upward to form an irreversible gel. Similarly, the aqueous extractitself may be heated to form the gel in ranges of I S to 50 percentsolids. We have discovered that aqueous suspensions of this type, whencoated upon paper, wood, and other surfaces, and dried are capable offorming a strong water-resistant bond by the application of heat andmild pressure.

A small amount of moisture appears necessary to form the heat-sealedbonds according to this nvention. Nevertheless, all seals which we havetested contained sufiicient moisture at equilibrium with the atmosphere.For all practical purposes the seals before heat energizing were dry tothe'touch, non-tacky, and non-blocking. The dry adhesive coating is nothygroscopic o-r sensitive to ordinary atmospheric conditions oftemperature or humidity. In this specification the term dry refers toair dry coatings, i. e., coatings that are at equilibrium with theatmosphere.

The temperature of sealing ranges from to 275 F. For smooth surfacecontacts, such metal-to-metal, metal-to-glass, paper-to-paper, and thelike, only slight pressure is required to insure satisfactory heatsealing. In the case of porous or uneven surfaces, such as wood,leather, fabric and the like, higher pressures are necessary to achievecontact during the sealing.

The application of the adhesive coating may be accomplished by means ofa 10 to '70 percent aqueous dispersion of the soybean protein substance.It may be brushed, poured, sprayed or otherwise coated on the surface,or articles to be coated may be dipped in the aqueous dispersion.

Our heat sealing process is not limited to the sealing of fiat or smoothsurfaces. It may be employed for bonding aggregates, such as corkgranules, wood or other fibers and the like. The coating suspensions maybe mixed or blended with other materials, such as starch, proteins,formaldehyde, dextrins, and resins to form air dry heat energizableadhesive coatings. In addition, any desirable filler or plasticizer maybe employed.

Since the air dry coatings have the dual property of being moisturesensitive (i. e., serve as remoistening adhesives), and heatenergizable, the seals may be made by first using the coating as aremoistening adhesive, as for example, in the sealing of an envelope,and subsequently allowing the seal to dry, then heat energizing the sealalready formed, as for example, by running a hot iron over the envelope.This procedure is convenient when desiring to make permanent andwater-resistant a seal which has already been formed. Moreover, articlesprepared for permanent sealing may be bonded lightly and/ or temporarilyemploying the remoistening property, and the temporarily bonded articlesmay be subsequently handled, transported, stored, and the like beforepermanent seals are made.

The following examples illustrate the invention.

EXAMPLE 1 The *gelable material was produced from hexane extractedsoybean flak-es by alcohol washing the flakes and subsequentlyextracting with water and spray drying the extract in accordance withthe disc'iosure in application Serial No. 782,941, previously mentioned.

, prefer a ratio of 3 to 16:1, by weight.

The sealing adhesive was made by applying a film of an aqueousdispersion of the gel material to the various surfaces and allowing thefilms to dry to equilibrium with the atmosphere. The dispersions were of48 percent solids. The samples of material were sealed in a Carver pressprovided with steam-heated platens. The results are summarized in thefollowing table.

1 Ddouble glue line, both surfaces coated; Ssingle glue line, onesurface coated.

3 The glue line darkened slightly with a few transparent spots,indicating some plastic flow under the conditions of the test.

3 Pressure of 2000 lbs. per sq. in.

4 A typical plywood application in that the center piece was coated oneach side-pressure of 4000 lbs. per sq. in.

5 Dried film flaked off where paper was not attached. Also, metal tometal because platen stuck to plate.

5 Oil oozed out of leather and the time was shortened.

In all cases the seals were stronger than the paper or wood bonded.

EXAMPLE 2 A 50-percent dispersion, made as in the above example, wascoated by brushing on two pieces of kraft paper, and the coatingsallowed to air dry over night. The two sheets were then placed with thecoated sides together and pressed with a moderately warm household iron.A strong water-resistant seal formed with amazing rapidity. The piecesof paper could not be torn apart without rupturing the paper.

In general the process of making the gelable material involves providingan alcohol-extracted proteinaceous soybean residue which issubstantially devoid of alcohol-soluble matter, extracting a sufficientquantity of this residue with water to obtain a mixture of aproteinaceous material suspended in an aqueous solution of water-solubleconstituents. The ratio of water to residue may vary over a wide range.We After removal of fibrous, insoluble soybean material, this mixturemay be dried, as by spray-drying to obtain a solid, powdery material.The mixture, or a similar water suspension of the dried material, gelsupon heating. The resulting product is an irreversible gel, and it, aswell as compositions comprising a substantial portion of it, retains itsshape indefinitely at all temperatures to which food products arenormally exposed.

The above-mentioned residue can be procured in either of two ways. Thefirst method is to treat a proteinaceous soybean material, which may beeither flakes, ground soybeans, or soybeans broken or comminuted in anyother fashion, to remove the oil. This may bedone by conventionalprocedures, such as by extraction with petroleum ether, hexane, or othersimilar solvent, by mechanical expulsion of the oil, and so forth. Theresulting oil-free, proteinaceous soybean material is then thoroughlycontacted with alcohol, such as by washing, to extract alcohol-solublematter.

We have found that washing with alcohol gives satisfactory results whenthe alcohol is employed in a concentration of about from 50 percent toabsolute alcohol. We prefer to wash With about 70 percent alcohol andattain improved results by repeating the wash.

The second method involves treating the soybean material, in any of theforms mentioned above, with alcohol directly to extract the oil and anyother alcohol-soluble matter present. Thus a secondary washing Withalcohol is unnecessary.

In both the above procedures, the use of alcohol, preferably ethylalcohol, has the effect of removing certain constituents among which arethose which act as antigelling factors and which heretofore haveprevented the formation of gels from proteinaceous soybean material.

An ideal material from which to obtain the gelling product is alcoholflakes, that is, flakes from which the oil has been extracted by ethylalcohol. Other flakes may be used, however, such as hexane-extractedflakes, flakes from which the oil has been expelled mechanically, andthe like. It is necessary in every case to remove the antigellingfactors by means of an alcohol wash. In the case of alcohol flakes,however, a secondary wash is not necessary since these factors have beenremoved along with the oil. High temperatures should be avoided duringprocessing for removal of the oil from the flakes.

In carrying out the process, the alcohol-exracted proteinaceous soybeanresidue prepared as described above, is mixed with water and is allowedto stand for a period of about one-half to one hour. Thereafter theinsoluble, fibrous material is separated from the aqueous phase byconventional procedure, such as filtration or other suitable methods.

The remaining aqueous phase may be evaporated, if desired, byconventional means, preferably by spray-drying, to produce the dry,solid, powdery gelling material. The aqueous phase itself, if iscontains at least 10 percent solids, or a similar water suspension ofthe dried product, will form the gel upon being heated.

In general, the content of solids ranges from about 10 to 50 percentwith respect to the Water content, and the gelling temperatures rangefrom F. to boiling, the higher temperatures corresponding to the lowerranges of solids content. For the purposes of this invention the contentmay range up to 70 percent.

The pH may vary over a wide range, but too great acidity will preventgelling and induce precipitation of the proteinaceous constituents. Ingeneral, the pH should be kept within the range of about from 5.0 to9.0.

The concentration of solids should be at least about 10 percent andpreferably above that in order to insure a satisfactory gel. Thiscorresponds to about 5 percent protein, since the protein content of thesolids varies from 50 to 60 percent. Higher concentration may be used asdesired.

The expressions water-extracted and mixing with water signify use ofordinary water and not aqueous protein denaturants.

The following tabulated example illustrates the gelling properties ofvarious concentrations of spray-dried solids added to water. In thesedata the material used was obtained by water extraction of alcoholflakes and contained about 54 percent protein. The pH of the aqueoussuspension was 0.0.

evaporated 5 volume.

10.0 percent solids added to water" Gel on boiling. 20.0 percent.solidsadded to water.- Gel at 200 F. 40.0 percent solids added to waterGel at 180 F.

Having thus described our invention, we claim:

1. A process of forming a water-resistant adhesive bond comprisingcoating the surface of material to be bonded with a to 70 percentaqueous dispersion of a gelable material hereinafter defined, drying thecoating to equilibrium with the atmosphere, the coating being dry to thetouch, non-tacky, non-blocking, and not sensitive to ordinaryatmospheric conditions of temperature or humidity, and thereafterapplying heat in the temperature range of 150 to 275 F. and pressing thecoated surface against another surface to bond the two together; saidgelable material being the water-extracted constituents of soybeanmaterial from which ethyl alcohol soluble anti-gelling substances hadbeen removed by extraction with ethyl alcohol.

2. Method of forming a water-resistant adhesive bond comprisingsubjecting contiguous articles, at least one of which is coated with anair-dry film of the water-extractable constituents of alcohol solublesfree soybean material to a temperature in the range of 150 to 275 F. andsufiicient pressure to insure contact between the articles, saidconstituents being the material obtained by extracting soybean materialwith alcohol to remove alcohol soluble antigelling factors, mixingtheresulting oil-free gellable material with water, and removing the waterinsoluble material.

3. Method of claim 2 in which both the articles have been previouslycoated and air dried, and

the contact is between contiguous coated sur- L faces.

6 4. In a method of bonding two surfaces by coating one or both of saidsurfaces with bonding material and applying heat and suflicient pressureto insure contact between the two surfaces, the improvement comprisingemploying as the bonding material an air dry film of an aqueous at leastten percent solids dispersion of a gelable material produced by treatingsoybean material to remove the oil and the alcohol-soluble material,extracting the residue with water, to separate the gelable material fromthe water insoluble portion of the residue.

5. In a method of bonding two surfaces by coating one or both of saidsurfaces with aqueous bonding material, permitting the material to dry,and thereafter pressing the surfaces together and applying heat to forma bond, the improvement comprising employing as the bonding material anair dry film of an aqueous at least about 48 percent solids dispersionof a gelable material produced by treating soybean material to removethe oil and the alcohol-soluble material, extracting the residue withwater, to separate the gelable material from the water insoluble portionof the residue.

ARTHUR C. BECKEL. JOHN C. COWAN. PAUL A. BELTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,851,952 Dike Mar. 29, 19322,200,839 Fleck May 14, 1940 2,229,028 Sturken Jan. 21, 1941 2,421,113Burnet et a1. May 2'7, 1947 2,495,706 Voss et al Jan. 31, 1950 OTHERREFERENCES Industr. and Engin. Chem., Soybean Protein, Smith and Max,July 1942, pp. 817 to 820.

4. IN A METHOD OF BONDING TWO SURFACES BY COATING ONE OR BOTH OF SAIDSURFACES WITH BONDING MATERIAL AND APPLYING HEAT AND SUFFICIENT PRESSURETO INSURE CONTACT BETWEEN THE TWO SURFACES, THE IMPROVEMENT COMPRISINGEMPLOYING AS THE BONDING MATERIAL AN AIR DRY FILM OF AN AQUEOUS AT LEASTTEN PERCENT SOLIDS DISPERSION OF A GELABLE MATERIAL PRODUCTED BYTREATING SOYBEAN MATERIAL TO REMOVE THE OIL AND THE AOCOHOL-SOLUBLEMATERIAL, EXTRACTING THE RESIDUE WITH WATER, TO SEPARATE THE GELABLEMATERIAL FROM THE WATER INSOLUBLE PORTION OF THE RESIDUE.